Trough-type parabolic concentrator

ABSTRACT

A trough-type parabolic concentrator (1) for a solar thermal power plant comprises a reflector plate (3) bent in trough shape and a support structure (4) for supporting the reflector plate (3) and comprising a plurality of wooden segments (2) arranged in a row in the longitudinal direction of the trough. Each segment (2) is assembled from a plurality of wooden frames (5). Using wooden frames (5) as the basic element of the supporting structure (4) allows for a lightweight, simple and low-cost structure of the trough-type parabolic concentrator (1).

BACKGROUND ART

The present invention relates to a trough-type parabolic concentratorfor a solar thermal power plant, which focuses incident solar radiationonto an absorber pipe in which a heat transfer medium flows that isheated by the concentrated solar radiation.

Parabolic concentrators of the trough type are implemented, for example,in so-called SEGS plants (Solar Energy Generating Systems) inCalifornia. The reflectors of these trough-type parabolic concentratorsare made of self-supporting composite glass silvered on the rear face.Therefore, the support structure for the reflectors only has to bear theweight of the reflectors; a shaping support of the reflector is notrequired. Due to the great effort of producing and mounting these powerplants, they operate economically only in the order of about 50 MW andmore. The investment required for a power plant of this caliber israther high, opposing the implementation of such power plants in varioussunny, but economically weak regions of the world.

In the past, efforts have been made to simplify the structure oftrough-type parabolic concentrators, so as to lower the costs for apower plant. As a reflector, thin anodized aluminum sheet was used,entailing a substantial reduction of weight compared to the silveredcomposite glass. There is a drawback, however, in that aluminum sheetdoes not have the self-supporting properties of composite glass. Thussupporting structures are required that support the aluminum sheet suchthat it is held in the parabolic shape. However, known supportingstructures of aluminum or steel are rather complex and heavy, which iswhy they are correspondingly expensive.

From U.S. Pat. No. 4,249,514, a solar concentrator of lightweightstructure comprising a plurality of adjacent segments is known. Eachsegment has two integral side members with stepped surfacesapproximating a curvilinear shape. Reflector bars are fixed on therespective steps of the two side members. On the rear, the side membersare supported by a truss structure. The truss structure is made of thinlongitudinal struts and tensioning wires fastened thereto. In this solarconcentrator, since the required shaping support for a reflector plateis not present, no continuous reflector plate can be installed thatwould have a better efficiency than single reflector bars. It is adisadvantage of the lightweight structure that the individual segmentsare not rigid in themselves so that each segment requires a supportfastened to the ground, requiring extensive structural efforts.

It is an object of the present invention to provide a trough-typeparabolic concentrator that has a simple stricture and may beimplemented economically.

SUMMARY OF THE INVENTION

The trough-type parabolic concentrator of the present inventioncomprises a reflector plate curved like a trough, which is preferablymade of anodized aluminum sheet or a sheet onto which thin glass mirrorsare adhered, and a supporting structure supporting the reflector plate,the structure comprising a plurality of wooden segments arranged in arow along the length of the trough. Each segment is composed of aplurality of wooden frames, the longitudinal and transverse bars of theframes supporting the reflector plate in a shaping manner. Using framesand segments provides for a modular structure of the trough-typeparabolic concentrator both in the longitudinal and the transversedirections, giving a high degree of flexibility in the design andrealization of the power plant. Since wood is a lightweight, easy towork and low-cost material and, further, wooden frames of relativelythin bars are used, weight and costs of the trough-shaped parabolicconcentrator can be reduced so that even smaller power plants can bemade to operate economically. Another advantage lies with the simplemounting of the trough-type parabolic concentrator, since, as a resultof the simple structure and the light weight of the wooden frames, evenlarge trough-type parabolic installations may be assembled almostentirely in situ so that transports of often rather large parts from theproduction site to the building site can be dispensed with. Due to theself-supporting frame structure of the trough-type parabolicconcentrator it is not necessary to set the trough-type parabolicconcentrator on supporting stands at each segment. Since the supportingstructure can transfer forces in any direction, supporting stands at theoutermost segments are sufficient.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a detailed description of an embodiment of the presentinvention with reference to the accompanying drawings.

In the Figures:

FIG. 1 is a perspective view of the trough-type parabolic concentrator,

FIG. 2 shows a cross-sectional view of the trough-type parabolicconcentrator,

FIG. 3 is a top plan view of a segment of the trough-type parabolicconcentrator,

FIG. 4 is a bottom view of the segment, and

FIG. 5 is a section along line IV--IV in FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In solar thermal power plants comprising trough-type parabolicconcentrators, incident solar radiation S is focused onto an absorberpipe A (FIG. 2) by means of trough-type parabolic concentrators 1. Aheat transfer medium, such as oil or water, which is heated by theconcentrated solar radiation and transported to a subsequent consumingdevice flows through the absorber pipe A. Typically, the width of theaperture of a trough-type parabolic concentrator is about 2 to 5 m,whereas the diameter of the absorber pipe is in the order ofcentimeters.

Referring to FIGS. 1-4, the structure of the trough-type parabolicconcentrator 1 will be described in more detail. The trough-typeparabolic concentrator 1 is divided into a plurality of segments 2(FIG. 1) in the longitudinal direction of the trough, i.e. in the axialdirection of the absorber pipe A. Each segment 2 has a reflector plate 3bent in trough-shape for focusing the incident solar radiation S ontothe absorber pipe A. The length of a segment 2, i.e. the dimension inthe longitudinal direction of the trough, is determined by the width ofthe material of the reflector plate 3. The reflector plate 3 is made ofa thin aluminum sheet of 0.5 to 1 mm in thickness, an anodized surfaceof the reflector plate 3 forming the actual reflector.

The reflector plate 3 is supported by a supporting structure 4. Thesupporting structure 4 of a segment 2 comprises a plurality of openboxes 5, open at the top and the bottom and made of plywood gluedtogether in a waterproof manner. The lateral bars of a frame 5 areinterconnected in comb-like engagement and may be given additionalrigidity by reinforcing angles provided on the inside. The surfaces ofthe frame 5 are sealed in a waterproof manner by a resin so as toguarantee long-time strength of the wood.

The frames 5 are designed such that, when assembled to form a segment 2,they define a parabolic top edge 11. The longitudinally extendinglongitudinal bars 6 of a box 5 are fixed to the transverse bars 7 at anangle such that their top edges 11 rest almost tangentially on thereflector plate 3. The top edges of the transverse bars 7 are in theshape of parable segments so that the assembled frames 5, with theirtransverse bars 7, form a parabolic trough onto which the reflectorplate 3 is placed so that the flexible reflector plate 3 is given itsshape by the longitudinal and transverse bars 6, 7 of the boxes 5. Theindividual boxes 5 are connected by screws 8. The surfaces of thenecessary bores are sealed with a resin to prevent humidity frompenetrating into the wood. The bottom side of each frame 5 has twodiagonally mounted metal bands 9 for reinforcing the frame.

FIG. 5 illustrates the joint between two segments 2 interconnected byscrews 10 extending through the transverse bars 7a, 7b of the frames 5.The parable segment-shaped top edges 11a, 11b of the transverse bars 7a,7b are coated with a layer 12 preventing the penetration of humidity. Atrough-shaped guide rail 13 for the reflector plates 3a and 3b,respectively, is fastened to the transverse bars 7a, 7b through screws14. The guide rail 13 is an aluminum profile and comprises an upwardprotruding web 15 embracing the reflecting surfaces of the reflectorplates 3a, 3b so that the reflector plates 3a, 3b are held in the guiderail and are forced to take a parabolic shape. At the outer transversebars 6 of a segment 2, the reflector plate 3 is secured against slippingfrom the guide rail 13 by stops of metal or wood. A reflectingself-adhering aluminum foil 17 is adhered on the top of the web 15 ofthe guide rail 13 so that even the solar radiation S impinging on theweb 15 is reflected onto the absorber pipe A.

When manufacturing the trough-type parabolic concentrator 1, first, thelongitudinal and transverse edges 6,7 of the frames 5 are cut to size,provided with comb-like teeth for assembly and with holes for thefastening screws 8 and 10, and shaped at their top edges 11 to take aparable segment shape. Subsequently, the bars 6, 7 are treated with aresin so that no humidity can penetrate into the wood. For the reflectorplates 3, anodized aluminum sheet is simply cut to size. These parts arethen transported to the building site where the solar thermal powerplant is to be erected.

When mounting the parts, first, the longitudinal and transverse bars 6,7are assembled into frames 5, e.g. by glueing, which are then reinforcedby metal bands 9. To mount a segment 2, the frames 5 are joined byscrews 8. Thereafter, the individual segments 2 are connected by screws10. The guide rails 13 for the reflector plates 3 are fastened on thetransverse bars 7 of the frames 5 of two adjacent segments. Finally, thereflector plates 3 are inserted into the guide rails 13 and securedtherein by stops 16.

Although the present invention has been described with reference to aspecific embodiment, a person skilled in the art will readily be able tomake modifications thereto to accommodate particular applications. Theseand other modifications are considered to fall within the scope of thepresent invention as defined by the appended claims.

What is claimed is:
 1. A trough-type concentrator comprising a supportstructure (4), said support structure (4) being constructed of aplurality of substantially identical segments (2), said segments (2)being arranged in immediately adjacent longitudinal lines, said segments(2) each being defined by a plurality of separate individual frames (5)in immediately adjacent transverse rows with each frame (5) including atleast two transversely spaced longitudinal bars (6) and at least twolongitudinally spaced transverse bars (7), means (8, 10, respectively)for interconnecting longitudinal bars (6) to each other and transversebars (7) to each other, and a separate individual reflector plate (3)spanning a plurality of said frames (5).
 2. The trough-type concentratoras defined in claim 1 wherein said transverse bars (7) are each of aparabolic shape corresponding substantially to a like parabolic shape ofsaid reflector plate (3).
 3. The trough-type concentrator as defined inclaim 2 including a second separate individual reflector plate (3)spanning another plurality of said frames (5), said reflector plates (3)including adjacent transverse edges (3a, 3b, FIG. 5), and transverselydisposed guide means (15) carried by selected ones of said frames (5)for retaining said adjacent transverse edges (3a, 3b).
 4. Thetrough-type concentrator as defined in claim 3 including means (16) atopposite ends of at least one transverse row for securing oppositelongitudinal edges of said reflector plate (3) to associatedtransversely opposite frames (5).
 5. The trough-type concentrator asdefined in claim 3 wherein each frame (5) is of a substantiallypolygonal configuration with adjacent longitudinal and transverse barsdefining corners thereof, and means (9) spanning selected diametricallyopposite corners for reinforcing an associated frame (5).
 6. Thetrough-type concentrator as defined in claim 3 including means (17) foreffecting reflection carried by said guide means (15).
 7. Thetrough-type concentrator as defined in claim 2 including means (16) atopposite ends of at least one transverse row for securing oppositelongitudinal edges of said reflector plate (3) to associatedtransversely opposite frames (5).
 8. The trough-type concentrator asdefined in claim 2 wherein each frame (5) is of a substantiallypolygonal configuration with adjacent longitudinal and transverse barsdefining corners thereof, and means (9) spanning selected diametricallyopposite corners for reinforcing an associated frame (5).
 9. Thetrough-type concentrator as defined in claim 1 including a secondseparate individual reflector plate (3) spanning another plurality ofsaid frames (5), said reflector plates (3) including adjacent transverseedges (3a, 3b, FIG. 5), and transversely disposed guide means (15)carried by selected ones of said frames (5) for retaining said adjacenttransverse edges (3a, 3b).
 10. The trough-type concentrator as definedin claim 9 including means (17) for effecting reflection carried by saidguide means (15).
 11. The trough-type concentrator as defined in claim 1including means (16) at opposite ends of at least one transverse row forsecuring opposite longitudinal edges of said reflector plate (3) toassociated transversely opposite frames (5).
 12. The trough-typeconcentrator as defined in claim 1 wherein said reflector plate (3) isan aluminum sheet having an anodized surface.
 13. The trough-typeconcentrator as defined in claim 1 wherein said reflector plate (3) isnon-reflective sheet metal having thin mirrors attached thereto.
 14. Thetrough-type concentrator as defined in claim 1 wherein each frame (5) isof a substantially polygonal configuration with adjacent longitudinaland transverse bars defining corners thereof, and means (9) spanningselected diametrically opposite corners for reinforcing an associatedframe (5).